A method for evacuating a package is known from EP0626312. In the known method an airtight package is pierced using a needle and vacuum is drawn through the aperture thus created. To this end a suction device is connected airtightly to a cover of a chamber in which the package is compressed prior to being evacuated.
Said method, however, has drawbacks. For evacuating the package, a chamber is required for accommodating and compressing the package. For larger packages, having a volume of for example 1000 litres, a large chamber is therefore required, which is impractical and requires expensive equipment (chambers).
U.S. Pat. No. 3,026,656 proposes to apply to the interior of a packaging film a label or reinforcing board such as cellophane or paper coated with a thermoplastic material, and comprising an aperture. The section of packaging film comprised within the perimeter of said label or reinforcing board comprises an aperture offset with respect to the label's aperture. A vacuum chamber is applied against the exterior of the packaging film at the location of the label, and air is withdrawn from the interior of the package by actuating a vacuum pump. The evacuation aperture in the packaging film can be sealed after evacuation by pressing a heated tool against the packaging film and label. The problem with this solution is that the label or reinforcing board are relatively flexible materials which cannot ensure a smooth enough contact surface for an air tight contact to be obtained with the vacuum chamber in case a relatively coarse granular product is contained in the package.
U.S. Pat. No. 3,026,656 proposes to apply to the interior of a packaging film a label or reinforcing board such as cellophane or paper coated with a thermoplastic material, and comprising an aperture. The section of packaging film comprised within the perimeter of said label or reinforcing board comprises an aperture offset with respect to the label's aperture. A vacuum chamber is applied against the exterior of the packaging film at the location of the label, and air is withdrawn from the interior of the package by actuating a vacuum pump. The evacuation aperture in the packaging film can be sealed after evacuation by pressing a heated tool against the packaging film and label. The problem with this solution is that the label or reinforcing board are relatively flexible materials which cannot ensure a smooth enough contact surface for an air tight contact to be obtained with the vacuum chamber in case a relatively coarse granular product is contained in the package. U.S. Pat. No. 3,216,172 proposes to solve the above problem by replacing the label or reinforcing board described above by a relatively stiff patch. The air in the package is evacuated through perforations in the patch, thus reaching an aperture in the packaging film. The perforation in the patch must be sufficiently fine to not allow the passage of the particles of the granulated or powdered bag content. The manufacturing of such patches can become problematic in case of applications with fine powders, and lead to unacceptably high pressure losses during evacuation of the package. Furthermore, this type of patches is prompt to clogging with granular or powdered materials: on the one hand, the finer the aperture (s) in the patch, the higher the risk of clogging by fine powders and, on the other hand, larger granules or particles can easily obstruct an aperture thus reducing the efficacy of evacuation or even stop stopping it altogether.
Furthermore, the existing systems allow a package to be evacuated once, which is thereafter irreversibly sealed by a hot sealing-device. It is, however, sometimes desirable to have a reversibly sealed package to allow multi-stages evacuation processes, and it can be necessary in certain cases to inject a gas into said package.
There therefore remains a need in the art for allowing rapid variation of the gas content and composition in a package, regardless of the size thereof, applicable to a broad selection of products to be packed, and requiring little investments and equipment of small size.